Automatic volume control circuit



Dec. 8, 1936. L. E. BARToN 2,063,577

AUTOMATIC VOLUME' CONTROL CIRCUIT I 'Filed DGO 16, 1935 ATTORNEY J 'L llw BY 2%' M Patented Dec. 8, 1936 PATENT OFFICE AUTOMATIC VOLUME CONTROL CIRCUIT Loy E. Barton, Collingswood, N. J., assignor to Radio Corporation of America, a corporation of Delaware Application December 16, 1933, Serial No. 702,714

10 Claims. (Cl. Z50-20) My present invention relates to amplifier control arrangements, and more particularly to a novel and improved arrangement for automatic volume control of a radio receiver.

f It is one of the main objects of my present invention to provide an automatic volume control system for a radio receiver wherein there is provided a normal bias for the controlled tubes which is greater than normal for the said tubes, the system utilizing a network of resistors in the grid return for the controlled tubes so that the high bias on the controlled tubes is bucked down to a normal value, the bucking current leaving the automatic volume control diode plate at a positive potential with respect to the cathodes of the controlled tubes.

Another important object of this invention is to provide an automatic volume control arrangement for a radio receiver so arranged that the output electrode for ythe automatic volume control will be positive with respect to the cathodes oi the controlled tubes under normal conditions, the volume control arrangement being additionally sol constructed that the tendency of the system tofiutter is reduced.

Another important object of the present invention is to provide an automatic volume control system for a radio receiver, wherein a diode is utilized as an automatic volume control element, and the diode anode, which delays the automatic' volume control action, is normally positive with respect to the cathodes of the controlled tubes until'the automatic volume control action is initiated.`

Still other objects of the .invention are'to improve generally the simplicity and efficiency oi automatic volume control arrangements, and to especially provide a superheterodyne receiver which embodies the improved type of automatic volume control arrangement in a compact and highly economical manner from the manufacturing viewpoint.

' The novel features which I believe to be characteristic of my invention are set forth in particularity in the appended claims. The invention itself, however, both as to its organization and method of operation, will best be understood by reference to the following description taken in connection with the drawing in which I have indicated diagrammatically a circuit organization whereby my invention may be carried into effect.

In the accompanying drawing there is shown a superheterodyne receiver of conventional form, and this receiver embodies the usual signal collector device A which may be the conventional grounded antenna circuit, a radio frequency signaldistribution line, or a loop antenna. The collected signals are fed into a radio frequency amplifier I, and the amplified radio frequency signals are then impressed upon a frequency changer network 2. The networks I and 2 may be given any form well known to those skilled in the art'. For example, the network I may be a tunable radii frequency amplifier, and the network 2 may embody separate first detector and local oscillator tubes. Alternately, thenetwork 2 may be a composite first detector-local oscillator network of the type disclosed by I-Iaines in his application Serial No. 663,171, filed March 28th, 1933, and in that case a gain control bias can be appliedto the signal grid of the composite first detector-local oscillator.

The. tuning means of the signal circuits and local` oscillation circuits of the networks I and 2 aenot shown, but those skilled in the art are well aware of the construction and know that there is .fed 'into the tuned circuit 2 energy of a substantially constant intermediate frequency. The intermediate frequency energy is then amplied in an intermediate frequency amplier which embodies a tube 3, and the latter is shown as of the 58 or pentode type. The tuned input circuit 4 of the amplier tube 3 is coupled tothe circuit 2', and th transformer 5, having a tuned primary and a tuned secondary, couples the anode circuit` of the amplifier tube 3 to the diode second detector circuit.

. VThe numeral designates an electron discharge'tube known as a duplex diode triode tube,

also known as a 55 type tube, and comprises with-` in a common tube envelope a triode section and a pair of diode sections. These sections use a common cathode, and the specific construction of the tube hasfbeen described and claimed by T. M. Shrader in his application Serial No. 622,140, filed July 12th, 1932. l

' `The diode anode 6 is connected to the cathode lead o f tube 55 through a path which includes the tunedinput circuit 5 and the resistor 2I connected` in series, the resistor 2l being shunted by radio frequency by-pass condenser 1 and the volume control comprising resistor network 'l and audio'by-pass condenser 2| The control grid of the triodesection of tube 55 is connected to the arm 9 of the volume control potentiometer 1 through a resistor 8. The audio frequency bypass condenser 2If connects the cathode side of potentiometer 'l to the cathode of the tube 55. The amplitude ofthe audio frequency component CIJ of the detected signal energy impressed upon the grid of tube 55 is controlled by the position of arm 9; however, it will be noted that the bias for the triode section of tube 55 is unchanged by the position of arm 9.

The remaining diode anode I0 functions as the automatic volume control element, and is connected to the positive side of the direct current power supply source through a path which includes lead II and resistor R3. The cathode of tube 55 is connected tothe negative side of the direct current power supply source through a path which includes lead I2 and resistor R5 in series. The direct current power supply source is of a conventional type too well known to those skilled in the art to require any further description. Between the positive and negative terminals of the source there is connected a path which includes the iron core choke coil I3 and resistor Re in series, the junction point of coil I3 and the resistor being grounded. The coil I3 is preferably the eld coil of the loud speaker.

The plate of tube 55 is connected to the positive terminal of the direct current power supply source through a path which includes resistor I4 and lead I5, a radio frequency by-pass condenser I6 being connected between the cathode and one side of resistor I4. An audio and radio frequency by-pass condenser I1 is connected between the cathode side of condenser I 6 and ground. Condenser I8 is employed to transmit the audio frequency signal energy in the plate circuit of tube 55 to the succeeding audio frequency amplifier; the latter may be a power tube if desired, and the amplified audio signal energy may then be reproduced by the loud speaker.

The automatic volume control path embodies the lead II, the resistor R2, and the lead 20 which is connected to the grid circuits of the controlled tubes. This path has been labelled AVC to clearly point out that this is the automatic volume control path. A resistor R1, in the case of the intermediate frequency amplifier tube 3, is connected between the lead 20 and ground, and the usual direct current blocking condenser 2I is connected between the cathode of tube 3 and the signal grid thereof. In the cathode circuit of tube 3 there is arranged a resistor having one side thereof grounded, the ground side of the resistor being connected to an adjustable tap 22 which is utilized to vary the magnitude ratios between the portions R4 and R7 of the resistor.

The type of automatic volume control arrangement shown in the aforedescribed circuit is described and claimed in my co-pending application Serial No. 640,946, filed November 3rd, 1932. One of the essential features of this type of automatic volume control arrangement is that no signal energy is directly impressed on the automatic volume control diode anode I0. Essentially, the automatic volume control action does not commence until the diode anode I0 is at least at cathode potential, and begins to perform its function when it becomes positive with respect to the cathode.

In other words, the diode which includes the anode I0 functions as a delay device for the automatic Volume control action until the intensity of signals impressed upon circuit 5 has assumed a value suicient to bring the potential of the cathode of tube 55 negative with respect to the diode anode I0. Normally, that is with no signals impressed upon the network 5', the potential of the cathode of tube 55 is positive with respect to the diode anode I0. As signals of proper intensity are impressed upon circuit 5 the grid of tube 55 becomes increasingly negative, and the flow of current through the space current path of the triode section of tube 55 decreases. This results in bringing the cathode potential negative with respect to the diode anode I0.

However, with no signal input to the receiver the diode anode I0 is positive with respect to the potential of the cathode of amplier tube 3. In the present application the potential relations between the diode anode I0 and the cathode of tube 3 will be discussed in detail, but it is to be clearly understood that the same explanation is to be considered as applicable to the circuits of networks I and 2, the latter not being shown in detail in order to simplify the present description. As soon as signals of the proper intensity are impressed upon the second detector circuit the potential of diode anode IU may become negative with respect to the cathodes of the controlled tubes. With no signals impressed upon the cir-- cuit 4 there is developed an abnormally high selfbias on the grid of tube 3. This is accomplished by properly choosing the values of the self-biasing resistor R1.

In order that the tubes I, 2 and 3 may have normal bias a current is caused to flow from the positive terminal of the plate supply through resistors R3, R2 and R1 so that there is sufcient positive potential across resistor R1 with negative potential at ground to reduce the abnormally high bias on the controlled tubes to normal values. Since the current through resistor R1 also passes through R2 there is a drop in this resistor greater than the normal bias of tubes I, 2 and 3. Therefore, the anode Ill is normally at a positive potential with respect to the cathodes of the tubes I, 2 and 3, the amplitude of which is a function of the relative values of resistors R1, R2 and R3. The following example will indicate practical operating voltages and resistor values when the potential value of the positive terminal of the power supply with respect to ground is about 254 volts. It will be noted that as the signal to the second detector increases so that automatic volume control voltage is applied to the radio frequency and intermediate frequency tubes, the potential of the cathodes of these tubes with respect to ground changes. This varying of potential further delays the action of the automatic volume control, and may be used for such functions as automatic selectivity control in cases where a potential opposite to the automatic volume control potential is desired.

Potential of cathode of tube 3 to ground=23 volts Drop across R1 at no signal=20 volts Therefore: normal bias for tube 3:3 volts R1 may be one megohm and R2=20,000 ohms then R3=approximately 12 megohms, and anode I 0 will be about one volt positive with respect to the cathode of tube 3.

It will, therefore, be seen that there has been provided by the present invention an automatic volume control arrangement for a radio receiver wherein the automatic volume control action is delayed until the signal intensity attains a desired value, this being accomplished by normally maintaining the volume control diode anode negative with respect to the cathode of tube 55. Furthermore, by the network of resistors described heretofore, and which network is used in conjunction with the automatic volume con-- 75A trol resistor in the grid returns for the control tubes, it is possible to maintain the automatic volume control anode I0 normally at a positive potential, that is in the no signal condition, with respect to the cathodes of the controlled tubes. This is generally accomplished by bucking down the abnormally high bias on the controlled tubes to a normal value, the bucking current leaving the diode anode l0 at a positive potential with respect to the cathodes of the controlled tubes.

While I have indicated and described a system for carrying my invention into effect, it will be apparent to one skilled in the art that my invention is by no means limited to the particular organization shown and described, but that many modications may be made without departing from the scope of my invention, as set forth in the appended claims.

What I claim is:-

1. An automatic volume control arrangement for a radio receiver which embodies a high frequency amplifier, a detector device coupled to the output of said amplifier, an electron discharge device having its grid connected to a point of audio frequency potential in the circuit of the detector, an anode disposed adjacent the cathode of the said electron discharge device, means for maintaining the cathode of the electron discharge device at a positive potential with respect to the said anode when no signals are impressed upon the detector, a direct current connection between the said anode and the grid circuit of said ampli- Iier, and resistive means electrically associated with the said anode to maintain the anode at a positive potential with respect to the cathode of the amplifier in the said no signal condition.

2. An automatic volume control arrangement for a radio receiver which embodies a high frequency amplifier, a detector device coupled to the output .of said amplifier, an electron discharge device having its grid connected to a point of audio frequency potential in the circuit of the detector, an anode disposed adjacent the cathode of the said electron discharge device, means for maintaining the cathode of the electron discharge device at a positive potential with respect to the said anode when no signals are impressed upon the detector, a direct current connection between the said anode and the grid circuit of said ampliiier, and resistive means electrically associated with the said anode to maintain the anode at a positive potential with respect to the cathode of the amplifier in the said no signal condition, said detector device comprisng an anode disposed adjacent said cathode, and both said devices and said first anode being included in a common tube envelope.

3. An automatic volume control arrangement for a radio receiver which embodies a high frequency amplifier, a detector device coupled to the output of said ampliiier, an electron discharge device having its grid connected to a point of audio frequency potential in the circuit of the detector, an anode disposed adjacent the cathode of the said electron discharge device, means for maintaining the cathode oi the electron discharge device at a positive potential with respect to the said anode when no signals are impressed upon the detector, a direct current connection between the said anode and the grid circuit of said ampli-- fier, and resistive means electrically associated with the said anode to maintain the anode at a positive potential With respect to the cathode of the amplifier in the said no signal condition, said resistive means being connected between the space current pathof the electron discharge device and the said grid circuit and being included in said direct current connection.

4. An automatic volume control arrangement for a radio receiver which embodies a high frequency amplifier, a detector device coupled to the output of said amplifier, an electron discharge device having its grid connected to a point of audio frequency potential in the circuit of the detector, an anode disposed adjacent the cathode of the said electron discharge device, means for maintaining the cathode of the electron discharge device at a positive potential with respect to the said anode when no signals are impressed upon the detector, a direct current connection between the said anode and the grid circuit of said amplifier, and resistive means electrically associated with the said anode to maintain the anode at a positive potential with respect to the cathode of the amplifier in the said no signal condition, said electron discharge device comprising an amplifier of the audio voltage developed by the detector, and the cathode of said electron discharge device becoming negative with respect to the said anode when signals are impressed on said detector.

5. In combination in a radio receiver, a high frequency amplifier provided with a resistor in its space current path,l the resistor being of a value suiiicient to provide a grid bias for the amplifier which is abnormally high, a rectifier coupled to the amplier output, a device of assymmetric conductivity including an anode electrically associated with said rectiiier, means operatively associated with the said device and resistor for reducing said high bias to a desired normal value land for maintaining said anode positive with respect to the amplifier cathode, and a direct current connection between said anode and the grid circuit of said amplifier.

6. In combination in a radio receiver, a signal transmission tube provided with a resistor in its space current path, the resistor being of a value sufficient to provide a signal grid bias for the tube which is abnormally high, a signal rectifier coupled to the tube output, a device of assymmetric conductivity operatively associated with said rectifier, and arranged to be conductive when signals above a predetermined amplitude are rectified, a direct current connection between a cold electrode of said device and the grid circuit of said tube, a source of direct current voltage, a resistive network connected to said source, connections from the grid circuit of said tube and and said resistor to said network such that said high bias is reduced to a desired operating value, and a connection from said cold electrode to a point on the resistive network such that the cold electrode is positive with respect to the cathode of said tube for signals less than said predetermined amplitude.

7. In combination in a radio receiver, a multiple duty tube comprising a pair of diode sections and a triode section, one of said diode sections being arranged to have signal energy impressed upon it and including a resistor in its circuit for developing a direct current potential component from the signal energy, the grid of said triode section being connected to a point of negative potential on the resistor, a high frequency ampli- Iier whose gain is to be controlled, a direct current connection between the grid circuit of said controlled amplifier and the anode of the second diode section, means in the space current path of the said triode section for maintaining the common cathode of said multiple duty tube at a positive potential with respect to the anode of the second diode section when no signals are received, and means electrically associated with the controlled amplier for maintaining the grid of the amplifier at an abnormally high bias with respect to the cathode thereof.

8. In combination in a radio receiver, a multiple duty tube comprising a pair of diode sections and an amplifier section, one of said diode sections being arranged to have signal energy impressed upon it and including a resistor in its circuit for developing a direct current potential component from the signal energy, the grid of said amplifier section being connected to a point of negative potential on the resistor, a high frequency amplier whose gain is to be controlled, a direct current connection between the grid circuit of said controlled amplier and the anode of the second diode section, means in the space current path of said amplifier section for maintaining the common cathode of said multiple duty tube at a positive potential with respect to the anode of the second diode section when no signals are received, means electrically associated with the controlled amplier for maintaining the grid of the amplier at an abnormally high bias with respect to the cathode thereof, and a plurality of resistors electrically associated with said direct current connection and the common cathode of the multiple duty tube for reducing said high bias to a normal value and for maintaining the second anode at a positive potential with respect to the cathode of the controlled amplifier.

9. In a, signaling system, a signal transmission tube having a cathode and control grid, a diode, means for maintaining the diode anode normally positive with respect to said transmission tube cathode, means for maintaining the control grid of the transmission tube normally at a desired operating negative bias with respect to the said cathode, means for causing said diode anode to become negative with respect to said cathode when signals are transmitted by said tube, and a direct current connection between said control grid and diode anode whereby the transmission eciency of said tube is automatically regulated.

10. In a signaling system, a signal transmission tube having a cathode and control grid, a diode, means for maintaining the diode anode normally positive with respect to said transmission tube cathode, means for maintaining the control grid of the transmission tube normally at a desired operating negative bias with respect to the said cathode, means for causing said diode anode to become negative with respect to said cathode when signals are transmitted by said tube, said last means normally causing the diode cathode to be positive with respect to the anode thereof, in the absence of signals, and a direct current connection between said control grid and diode anode whereby the transmission efliciency of said tube is automatically regulated.

LOY E. BARTON. 

